Having lived in Italy I've seen many many racehorses going off to slaughter, straight off the track, regardless of what the passport says. There are killbuyers who have tons of passports who fit just about any horse out there. Apparently chip controls are rather rare at slaughter facilities.
I wouldn't have my horse sent off to slaughter, but I see the need for slaughter facilities.
As long as there is a greater supply than demand, they unwanted ones have to go somewhere.
The demand for horsemeat is there, Italy even breeds for slaughter.
I remember small butchershops in Germany for horses only, and the butcher would either let the owner hold the horse for the shot or hand him the halter right after the kill. Some of them even would come out to the owners place with a trailer, load the horse, shoot it, bleed it and take it away. Least stress and one can be sure the horse doesn't go on a long grueling trip to eventual death.